The present invention relates toward an inventive oven for curing coatings applied to an object. More specifically, the present invention relates to a convection combustion oven having a simplified design for curing coatings applied to an object.
Various types of ovens are used to cure coatings, such as, for example, paint and sealers, that are applied to articles in a production setting. One example is decorative and protective paint that is applied to automotive vehicle bodies in a high volume paint shop known to process vehicle bodies at rates exceeding one per minute.
A typical oven uses combustion fuel to provide the necessary amount of heat to cure paint applied to a vehicle body. Generally two types of ovens are presently used, a convection oven and a radiant heat oven. Occasionally, a combination of convection and radiant heat is used in a single oven to meet paint curing specifications. A convection heat oven makes use of a heat source such as natural gas flame that heats pressurized air prior to delivering the heated air to an oven housing. A first type of convection heating applies combustion heat directly to pressurized air prior to delivery to the oven housing mixing combustion gases with the pressurized air. A second type of convection heating uses an indirect heating process where combustion heat is directed into a heat exchanger that heats the pressurized air without mixing the combustion gases with the pressurized air.
An alternative source of heat is provided inside the oven housing by a radiant heater that transfers heat to the vehicle body by way of proximity to the vehicle body. As known to those of skill in the art, a radiant heater is generally a metal panel that is heated by circulating hot air into a space located behind a radiator.
The conventional convection and radiant ovens have proven to be exceedingly expensive to construct and do not provide energy efficiencies desirable in today's high-cost energy market. A conventional oven design is generally shown at 10 in FIG. 1. The conventional oven assembly 10 generally includes two main components, a heater box 12 and an oven housing 14. The heater box 12 is generally spaced from the oven housing 14 and includes components (not shown) to provide heat and pressurized air to the oven housing 14 through hot air duct 16. The heater box 12 includes a return duct that draws a significant portion of air from the interior of the oven housing 14 for recirculation through the oven housing 14. Up to ninety percent of the air passing through the heater box 12 is derived from the interior of the oven housing 14 through return duct 16. Generally, only ten percent of the air delivered to the oven housing 14 through hot air duct 16 is fresh air drawn from outside the oven housing 14. Hot air is directed through hot air headers 20 toward the vehicle body through nozzles 22 to optimize a uniform heat transfer to cure the coating applied to the vehicle body. Generally, the vehicle body is heated to about 275-340° F. at a predetermined time to adequately cure the applied coating. Some coatings, such as electrodeposition primers, require temperatures at the higher end of this range. As is known to those of skill in the art, more heat must be directed toward heavy metal areas of the vehicle body to derive the desired baking temperature.
A typical oven zone of about eighty feet in length of a conventional oven requires an actual air volume of about 30,000 cfm when using a heater box. This high air volume is required to transfer the necessary heat to the vehicle body to cure the applied coating. The air temperature at the nozzle 22 in a conventional oven is generally 444° F. requiring an air velocity at the nozzle 22 of 4,930 fpm to transfer the desired amount of heat energy. The operating parameter set forth above generally provides 1,595,000 BTU/hr at a momentum of 4.9×106 ft-lb/sec2. Because hot air is recirculated by the fan located in the heater box 12, and because the recirculated air is often reheated prior to being pressurized by the fan, the fan requires an overlying robust design adding to operation and installation costs.
The volumes and flow rates presently used in conventional ovens require heavy duty fans and heater systems that are not believed necessary to obtain the required heat transfer. This is in part due to the recirculation of hot air through the fan and back into the oven housing 12. Furthermore, due to the recirculation, a substantial amount of insulation 24 is required around the heater box 12 and the hot air duct 16 to reduce heat loss and protect workers from physical contact. Therefore, it would be desirable to design a simplified oven assembly that does not require extensive insulation and complex apparatus associated with conventional heater boxes.